2019年英语六级考试阅读外刊1

坦途网英语六级考试频道在本文将为您分享英语六级考试阅读理解技巧，帮助各位即将考试的学子们在阅读题中获得高分。说起阅读，很多同学也会经常看相关材料，但是阅读题的分数却一直没有提高，其实主要原因就在于看的东西太杂，不利于形成系统化的知识。

Why do cats—and so many other animals—look like they’re wearing socks?

What do all of the internet-famous cats have in common? From ankle down, their paws are as white as the trends vying （竞争）for attention in the very same Instagram feed.

Pet lovers refer to this particular color pattern as an animal’s “socks," “booties,” "mittens," or "tuxedo" for obvious reasons. Thephenomenon of pigment （色素） mixed with white spots can occur in pigs, deer, horses, dogs, guinea pigs, birds, and, in rare cases, humans. But it’s particularly prominent in cats, as evidenced by the fact that Socks consistently ranks in the top names for cats.

But scientists have another name for it: piebaldism（斑驳病）. It’s the result of a mutation in the KIT gene, which causes an unusual distribution of melanocytes—the cells that give eyes, skin, and hair or fur pigment.

When a cat is still an embryo, all of its available melanocytes are bunched up toward its back, where its spinal column will eventually form. As the fetus develops into a kitten, pigment cells spread throughout the developing body. If the melanocytes are evenly distributed, the cat could have a one-colour coat. But in many animals, the cells spread irregularly. That’s how you get a cat like Sylvester, who’s black from his back to his legs, but white down to his toes.

Why exactly the melanocytes clump and cluster has been a matter of some debate. It was long thought that the cells just didn’t move at the right rate to completely cover an animal’s body. But more recent research in Nature Communications using a mathematical model of melanocytes suggests that the pigment cells in piebald animals don’t divide often enough, leaving the developing critter without enough biological material for a single-colour coat.

Piebaldism isn’t the only genetic coincidence that can alter an animal’s fur, according to the UC Davis Veterinary Genetics Lab. The tabby cat’s signature look is served up by the agouti gene, which determines the distribution of black pigment. The same gene gives rise to “bay” horses, which have brown bodies, but pitch black manes and tails. Norwegian Forest cats harbor two mutations of note: The aptly-named “Orange gene” on the X chromosome （染色体） can produce a red coat in many cats, but an alteration on the MC1R gene appears specific to this breed. Born one color, these felines can mature into another golden or “amber” hue. And Siamese and Burmese cats have a form of selective albinism （白化病） that allows them to suppresspigment production based on temperature. The activating chemicalexplains the Siamese's unique appearance, with its sandy-colored abdomen (the warmest part of the body) th

2019年英语六级考试即将到来，希望本篇资讯能够为大家带来一定的帮助。本篇分享内容是“主题阅读”材料，通过这种主题阅读方式记忆效果更好，学习者更加容易学以致用。并且对于主题阅读来说外刊是很好的选择，外刊不仅可以积累相关的知识，还可以很好的扩充你的词汇量和丰富你的知识面。